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Yesterday I was watching discovery channel, on a program they said that 'if two pieces of the same type of metal touch in space, they will be permanently stuck to each other.' Is it true..? If yes... then how is it so? Why is it not possible on Earth?

Kyle Oman
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nitin yadav
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  • It is not true that this happens spontaneously, but on the other hand one can use the effect on earth and it is being used for some applications... with extremely parallel surfaces that have been cleaned from all molecular layers in vacuum. It's usually not a problem, until it is, which is one reason why we use HV lubricants in high-vac applications, just to make sure that it doesn't happen when we don't want it. – CuriousOne Jun 09 '16 at 06:55

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Phenomena is called Cold Welding

The reason for this unexpected behavior is that when the atoms in contact are all of the same kind, there is no way for the atoms to “know” that they are in different pieces of copper. When there are other atoms, in the oxides and greases and more complicated thin surface layers of contaminants in between, the atoms “know” when they are not on the same part.

— Richard Feynman, The Feynman Lectures, 12–2 Friction

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It all depends on how clean the surface of the metal are. If there are oxides and impurities on the surfaces they will not bond together. However if the surfaces are ultra clean with no gas molecules from the atmosphere adhering to them, which on Earth would require them to be an ultra high vacuum chamber, then the surfaces would join together having made metal to metal bonds.

Farcher
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